The surface characteristics of a substrate can be altered by a variety of means, perhaps most readily by the application of a coating layer. For example, the frictional properties or adhesive properties of materials can be modified, depending on the desired use of the materials, by suitable treatment of their surface. A number of methods for altering the surface properties of polymeric biomaterials, such as contact lenses, and for coating electronic devices have also been developed. Water repellant, oil repellent, stain resistant, anti-microbial, anti-static, anti-fog, anti-scratch and water absorptive surface treatments and coatings are well known commercial products.
U.S. Pat. No. 7,122,599, incorporated herein in its entirety by reference, discloses coating compositions and polymeric molding compounds having anti-adhesion and dirt repellency properties. The compositions contain as an additive a branched polymer which comprises a polymeric base molecule and polydiorganosiloxane side chains which are bonded covalently to the base molecule via Si—C bonds.
U.S. Pat. No. 6,641,870, incorporated herein in its entirety by reference, discloses a process for producing a coating, i.e., an ink or paint or a pollutant, bioorganism, oil, water and/or dirt repellent coating, on a substrate, which process comprises first applying to a substrate a composition which includes one or more organosilicon components to obtain a treated substrate and subsequently applying at least one organosiloxane (i) which carries at least one select triamino group or a composition which includes at least one organosiloxane (i), to the treated substrate. Said coating provides protection against water-transported pollutants and furnishes the substrate with anti-graffiti properties.
U.S. Pat. No. 6,811,884 incorporated herein in its entirety by reference, discloses a method for applying a water repellant coating over a substrate surface wherein the surface is contacted with at least one coating composition comprising at least one perfluoroalkylalkylsilane, at least one hydrolyzable primer, e.g., a silane and/or siloxane, and at least one non-halogenated, e.g., non-fluorinated, alkylsilane.
In many cases it is important for both economic and performance reasons to produce thin, defect-free, mono- or multi-layer coatings. It is also desirable that the layers are durable under the conditions where the coated substrate is used.
There are several known methods for the preparation of ultra thin mono- and multi-layered films including solution casting, Langmuir-Blodgett technique and various chemisorption techniques. While each method has advantages, there are also disadvantages when a particular method is used in certain applications. For example, solution casting of preformed bilayer aggregates and annealing of spin coated films of copolymers yields layered structures, but the alignment of the layers and the positioning of molecules with respect to each other is limited. Chemisorption methods typically require exacting conditions and often multiple chemical reactions.
U.S. Pat. No. 5,208,111, incorporated herein in its entirety by reference, discloses a method for applying one- or multi-layered layer elements to supports via the alternating deposition of polycations and polyanions. For example, a positively charged glass substrate is first created by suitable silane chemistry, then immersed into a dilute solution of a polyanion which is then immersed in a dilute solution of a polycation. Repetition of this cycle produces a multilayer thin film comprised of alternating layers of polycations and polyanions wherein the thickness and conformation of each polymer layer is determined by the chemistry and concentration of the depositing solution.
U.S. Pat. No. 5,518,767, incorporated herein in its entirety by reference, discloses a molecular self-assembly process based on the alternating deposition of a p-type doped electrically conductive polycationic polymer and a conjugated or nonconjugated polyanion similar to U.S. Pat. No. 5,208,111. In this process, multilayer thin films are prepared by alternating the deposition of a monolayer of an electrically conductive polymer with the deposition of polyanion layer from dilute solutions. Multilayer thin films are obtained by repeating the process. In contrast to a deposition process involving the alternate self-assembly of polycations and polyanions, this process is driven by the electrostatic attractions developed between the p-type doped conducting polymer and the polyanion.
Many of these coating methods, in particular for coating glass and ceramics, require complex and time-consuming pretreatment of the substrate to produce a surface having a highly charged, hydrophilic, or hydrophobic nature in order to bind the polycationic or polyanionic material to the glass substrate.
In preparing coatings comprising inorganic particles, such as metal oxide nano-particles, it is desirable that the particles are evenly dispersed over the surface without particle agglomeration. Organic materials, such as the polymers found in the art cited above, can also be used to prepare coating layers comprising evenly dispersed inorganic particles using the techniques described therein, including the sequential application and self assembly of materials from different solutions and suspensions. Direct vapor deposition of inorganic particles is often encountered in the application of coating layers consisting predominately or exclusively of inorganic materials, such as layers of metal and/or metal oxide nanoparticles.
Improved methods are still needed for the preparation of high quality, durable, metal oxide layers on substrates such as glass or ceramics. It has been found that coatings of evenly dispersed metal oxides can be conveniently prepared on a variety of substrates including glass and ceramics without the use of specialized equipment.
A simple, inexpensive and versatile method has been discovered which allows for control of the thickness of metal oxide layer and reproducibly provides metal oxide layers with excellent surface characteristics. The method makes use of simple, known coating techniques to prepare a metal oxide/organic polymer precursor coating layer on the substrate which is then converted by calcining to a high quality layer of predominately or exclusively metal oxide. Hydrophilic surface layers, which are often scratch resistant, stain resistant and easy to clean, are thus produced on non-hydrophilic substrates.